The present invention relates generally to the field of magnetic data storage and retrieval. In particular, the present invention relates to a magnetic recording head having recessed top and bottom shields.
In a magnetic data storage and retrieval system, a magnetic recording head typically includes a reader portion having a magnetoresistive (MR) sensor for retrieving magnetically-encoded information stored on a magnetic disc. Magnetic flux from the surface of the disc causes rotation of the magnetization vector of a sensing layer of the MR sensor, which in turn causes a change in electrical resistivity of the MR sensor. The change in resistivity of the MR sensor can be detected by passing a current through the MR sensor and measuring a voltage across the MR sensor. External circuitry then converts the voltage information into an appropriate format and manipulates that information as necessary.
MR sensors fall generally into two broad categories: (1) anisotropic magnetoresistive (AMR) sensors and (2) giant magnetoresistive (GMR) sensors. AMR sensors generally having a single MR layer formed of a ferromagnetic material. The resistance of the MR layer varies as a function of cos2xcex1, where xcex1 is the angle formed between the magnetization vector of the MR layer and the direction of the sense current flowing in the MR layer.
GMR sensors have a series of alternating magnetic and nonmagnetic layers. The resistance of GMR sensors varies as a function of the spin-dependent transmission of the conduction electrons between the magnetic layers separated by the nonmagnetic layer and the accompanying spin-dependent scattering which takes place at the interface of the magnetic and nonmagnetic layers and within the magnetic layers.
GMR sensors using two layers of ferromagnetic material separated by a layer of nonmagnetic electrically-conductive material are generally referred to as spin valve (SV) sensors. The layers within a SV sensor include a nonmagnetic spacer layer positioned between a ferromagnetic pinned layer and a ferromagnetic free layer. A magnetization of the pinned layer is fixed in a predetermined direction, typically normal to an air bearing surface of the SV sensor, while a magnetization of the free layer rotates freely in response to an external magnetic field. An antiferromagnetic material is typically exchange coupled to the pinned layer to fix the magnetization of the pinned layer in a predetermined direction, although other means of fixing the magnetization of the pinned layer are available.
GMR sensors using two layers of ferromagnetic material separated by a layer of nonmagnetic electrically-insulating material are generally referred to as spin-dependent tunnel junction (STJ) sensors. The layers within a STJ sensor include an ultra-thin tunnel barrier layer positioned between a ferromagnetic pinned layer and a ferromagnetic free layer. As in the SV sensor, a magnetization of the pinned layer is fixed in a predetermined direction, typically normal to an air bearing surface of the STJ sensor, while a magnetization of the free layer rotates freely in response to an external magnetic field. An antiferromagnetic material is typically exchange coupled to the pinned layer to fix the magnetization of the pinned layer in a predetermined direction, although other means of fixing the magnetization of the pinned layer are available.
Shields are generally placed on either side of the MR sensor to ensure that the MR sensor reads only that information which is stored directly beneath it on a magnetic medium or disc. To allow for a greater amount of magnetic flux to be sensed by the MR sensor, the MR sensor is typically positioned such that one surface of the MR sensor is exposed at an air bearing surface (ABS) of the magnetic recording head.
There are several problems associated with this placement of the MR sensor at the ABS. First, the exposed surface of the MR sensor may corrode, leading to sensor failure.
Second, the MR sensor may collide with the magnetic media due to low fly heights, magnetic media asperities or a warp in the surface of the magnetic media. Such collisions can cause the temperature of the MR sensor to increase, thereby affecting the resistance of the MR sensor and causing sensor failure.
Third, the MR sensor may be damaged during the processing of the magnetic recording head, particularly during the lapping of its ABS surface due to the MR sensor also being lapped. One problem associated with the lapping of the MR sensor is that it is important to control the stripe height of the MR sensor to a tolerance greater than allowed by the lapping process. A second problem associated with the lapping of the MR sensor is specific to STJ sensors which should not be lapped due to the very thin barrier layer, the lapping of which will likely result in a short between the two ferromagnetic layers.
The fourth problem associated with the placement of the MR sensor at the ABS is specific to STJ sensors. The resistance of an STJ sensor is inversely related to the area of the sensor (the sensor length multiplied by the sensor width). As STJ sensor widths continue to decrease to achieve the necessary higher recording densities, the sensor length must increase to maintain a constant resistance of the sensor. However, it is difficult to increase the effective length of an STJ sensor placed at the ABS (the effective length being the length of the sensor actually affected by the magnetic flux from the disc). Accordingly, as the width of STJ sensors continues to decrease, the resistance of the sensor will continue to increase, thus requiring the invention of new electronics to convert the read signal of the higher impedance sensor.
To overcome the above-recited problems, magnetic recording heads having a recessed MR sensor have been pursued as alternatives to magnetic recording heads having the MR sensor positioned at the ABS. However, the amount of magnetic flux sensed by the MR sensor diminishes as the MR sensor is moved from the ABS. To increase the amount of flux that reaches the MR sensor, a first flux guide, which extends from the ABS toward the MR sensor, may be used to carry magnetic flux from the ABS to the M sensor. To increase the effective stripe height of the MR sensor, a second flux guide extending from the MR sensor away from the ABS may be added to the recording head to carry flux toward a back edge of the MR sensor. Rather than having two separate flux guides, a single flux guide extending from the ABS toward the back of the MR sensor may replace both the first and second flux guides.
Although the first and second flux guides increase the amount of magnetic flux that reaches the MR sensor, a substantial amount of magnetic flux is still leaked into the top and bottom shields because of the close proximity of the shields to the flux guides and the MR sensor. For the shields to be effective, the gap at the ABS between the top and bottom shields is limited by the bit density of the magnetic media to ensure that the MR sensor receive magnetic flux from only a single transition on the media. The gap between the MR sensor and the top and bottom shields is similarly limited. Because of this smaller gap between the MR sensor and the top and bottom shields, magnetic flux is likely to exit the flux guide and enter the top or bottom shield.
To decrease the amount of magnetic flux leaked into the top and bottom shields, magnetic recording head designers have begun incorporating recessed shields with recessed MR sensors. Recessed shields are shields which have been shaped to have a small read gap between themselves at the ABS and to have a large cavity between themselves away from the ABS. The MR sensor is placed in the cavity.
These recessed shields generally have a non-recessed portion adjacent the ABS and a recessed portion opposite the ABS. The narrow read gap is defined between the non-recessed portions of the top and bottom shields, while the large cavity in which the MR sensor is placed is defined between the recessed portions of the top and bottom shields. In this recessed shield design, there is a larger gap between the MR sensor and the top and bottom shields, thereby minimizing the amount of flux that will escape to the shields.
For recessed shields to be advantageous over non-recessed shields, the length of the non-reccssed portion needs to be large enough that the shield can absorb the stray magnetic flux from adjacent transitions on the magnetic media to prevent the MR sensor from reading the stray data. Additionally, the non-recessed portion length needs to be small enough that the amount of magnetic flux exiting the first flux guide and entering the top and bottom shields is minimized. If the non-recessed portion length is too large, much of the magnetic flux will have leaked into the top and bottom shields before it reaches the recessed portion of the shields, thereby eliminating any advantage gained by the use of recessed shields.
The effective non-recessed portion length of a magnetic recording head having top and bottom recessed shields is the larger of the non-recessed portion lengths of the top and bottom shields. Because it is generally desired that the non-recessed portion length be as short as possible, it is important that the non-recessed portion lengths of the top and bottom shields be substantially equal to one another.
Recessed shields typically are shaped by photolithography. This process, however, is limited in the amount of control over tolerance that can be exerted. Therefore, there is a need for a recessed shield design that allows for greater control of the non-recessed portion lengths of both the top and bottom shields to ensure their substantial equality.
A method for forming a transducing head first requires the deposition of a bottom shield, a bottom thick gap, a bottom thin gap, a sensor, a first flux guide, a top thin gap, a top thick gap, and a top shield. After each of the layers is deposited, an air bearing portion of both the top and bottom thick gaps is removed, such that a length of the air bearing portion of the top thick gap is substantially equal to a length of the air bearing portion of the bottom thick gap. Next, an air bearing shield is deposited over the air bearing surface, the air bearing shield being in contact with the top and bottom shields, the top and bottom thick gaps, the top and bottom thin gaps, and the flux guide. Finally, the air bearing surface of the transducing head is planarized, resulting in the top and bottom thin gaps and the first flux guide each being exposed at the air bearing surface.